Complete Guide to COA Verification for Engineered Stone Alternatives
A Certificate of Analysis (COA) is a supplier’s formal statement that a specific batch of product meets defined specifications. For silica-free surface materials, the COA is often the key piece of documentation that determines whether a shipment clears customs, passes a project inspection, or triggers a regulatory violation. Here’s how to read one and what to demand from your suppliers.
What a COA Should Include
| COA Element | Why It Matters |
|---|---|
| Batch/lot number | Must match the batch number on your order, invoice, packaging, and slab labels. A COA without a batch number isn’t a COA — it’s a brochure. |
| Production date | Should be within a reasonable window of your order. A COA from a batch produced 18 months ago may not represent the current formulation. |
| Specification tested against | What standard or specification does this COA certify against? “Meets silica-free requirements” is not a specification. Cite the actual standard or threshold. |
| Test method | What method was used? XRD (quantitative), FTIR (qualitative), optical microscopy (observational only)? XRD with quantification is the only method accepted for silica content certification. |
| Test results (numerical) | Actual numbers, not “pass/fail.” For silica: crystalline silica content as weight percentage, with detection limit stated. |
| Testing laboratory | Name, accreditation (ISO 17025), analyst name, date of analysis |
| Authorised signature | Signed by an authorised representative of the manufacturer or testing laboratory |
A warning from experience: We once saw an importer receive a COA stating “0% crystalline silica” for a container of quartz slabs. The COA had a batch number, a signature, and looked professional. But the lab name was a manufacturer-owned facility with no ISO 17025 accreditation. Independent testing later showed 92% crystalline silica content. The COA wasn’t fraudulent — the manufacturer simply tested the resin component (which was silica-free) and issued the COA as if it represented the whole product. Always check what was actually tested.
COA Red Flags
- Generic/template COA with no batch-specific data — not a valid COA
- “Pass” or “Complies” without numerical results — ask for the actual measurement
- No test method specified — how can you verify the result?
- Testing conducted by manufacturer without independent verification — request third-party testing for critical parameters like silica content
- COA more than 12 months old — formulations, raw material sources, and manufacturing parameters change
- No link between COA batch number and physical product markings — without traceability, the COA is worthless
Building a COA Verification System
For importers and distributors handling multiple suppliers:
- Require COA before shipment. Don’t accept a COA that arrives with the container — by then it’s too late to reject.
- Verify one COA per batch, per colour. A single COA for “all our products” is not acceptable. Each colour, each production batch requires its own COA.
- Spot-check with independent testing. Send random samples to an ISO 17025 accredited lab for independent silica content analysis. If the independent results don’t match the supplier’s COA, you have a systemic problem.
- Maintain a COA database. Keep all COAs organised by supplier, product, batch, and date. When a regulator, insurer, or customer asks for documentation, you need to find it in minutes, not days.
For a complete documentation framework, see our Silica-Free Sourcing Checklist.
COA Verification Checklist
Free: 10-point COA verification checklist with supplier request templates.
Sources & References
Complete numbered source list with URLs available to subscribers.
